Prewarning device for induction melting furnace

Abstract

A prewarning device for an induction melting furnace serves for warning of breakouts of molten metal on ceramic furnace linings of melting furnaces. The device has electrodes that may be arranged on the furnace lining in question which are divided into two groups of different polarity and are spaced apart from each other. The electrode groups can be connected to an evaluation unit in order to determine the electrical temperature-dependent resistance of the furnace lining. In order to permit a simple application of the electrodes on the outside of the furnace lining and assure a high reliability of indication of the entire system, at least a high reliability of indication of the entire system, at least one of the electrodes is arranged as an electrode network on a first side on a ceramic foil. Either the first side of the ceramic foil or the opposite side is arranged on the furnace lining. The foil in the former case has a lower thermal conductivity and a lower electrical conductivity than the ceramic material of the furnace lining and in the latter case an approximately identical or higher thermal conductivity and an approximately identical or higher electrical conductivity.

What is claimed is: 
     
       1. A warning device for detecting leakage of molten metal through a substantially ceramic lining mounted inward of a coil of an induction furnace, the device comprising electrodes mounted on a ceramic foil positioned between the lining and the coil, the electrodes arranged in two networks with each of the networks having a different polarity from the other and each of the networks connected to an evaluation unit for determining electrical temperature-dependent resistance at the lining located within the networks, at least one of the networks arranged on a side of the foil facing the lining and in intimate contact with the lining, material of the foil selected to provide it with lower thermal and electrical conductivities than of the lining. 
     
     
       2. A warning device for detecting leakage of molten metal through a substantially ceramic lining mounted inward of a coil of an induction furnace, the device comprising electrodes mounted on a ceramic foil positioned between the lining and the coil, the electrodes arranged in two networks with each of the networks having a different polarity from the other and each of the networks connected to an evaluation unit for determining electrical temperature-dependent resistance of the lining located within the networks, at least one of the networks arranged on a side of the foil away from the lining, material of the ceramic foil selected to provide it with higher thermal and electrical conductivities than of the lining. 
     
     
       3. The warning device as claimed in claim 1, with material of the foil selected to provide it with a lower specific electrical resistance than that of the lining. 
     
     
       4. The warning device as claimed in claim 2, with material of the foil selected to provide it with a higher specific electrical resistance than that of the lining. 
     
     
       5. A warning device for detecting leakage of molten metal through a substantially ceramic lining mounted inward of a coil of an induction furnace, the device comprising electrodes arranged in two networks with each of the networks having a different polarity from the other and each of the networks connected to an evaluation unit for determining electrical temperature-dependent resistance of the lining located within the networks, at least one of the networks arranged between an inner foil and an outer foil with both of the foils positioned between the lining and the coil, the inner foil maintained in intimate contact with an outer surface of the lining and made of a material having higher thermal conductivity and lower specific electrical resistance than the material of the lining, the outer foil made of a material having lower thermal conductivity and higher specific electrical resistance than the material of the lining. 
     
     
       6. The warning device as claimed in claim 5, wherein the inner foil and the outer foil and said at lest one of the networks are organized as a prefabricated mat ready for installation, at least one lead connected to and extending from said at least one of the networks. 
     
     
       7. The warning device as claimed in claim 1, with a plurality of the ceramic foils each having arranged thereon one of the electrode networks, at least one lead connecting each of the networks to the evaluation unit. 
     
     
       8. The warning device as claimed in claim 1, with said networks acted upon by alternating voltage. 
     
     
       9. The warning device as claimed in claim 1, with said networks acted upon by a sinusoidal alternating voltage with a frequency between 20 and 30 Hz. 
     
     
       10. A warning device for detecting leakage of molten metal through a substantially ceramic lining mounted inward of a coil of an induction furnace, the device comprising a ceramic foil positioned between the lining and the coil and provided with an outer surface facing away from the lining, electrodes arranged on said outer surface and subdivided into two networks with each of the networks having a different polarity from the other and each of the networks connected to an evaluation unit for determining electrical temperature-dependent resistance of the lining located within the networks, material of the foil selected to provide higher thermal and electrical conductivities than of the lining, the electrodes of said networks are arranged in interengaged comb shaped with equal distances from each other.